Phosphonate polymers, copolymers, and their respective oligomers as flame retardants for polyamide fibers

ABSTRACT

The invention relates to the use of polyphosphonates, copoly(phosphonate ester)s, copoly(phosphonate carbonate)s, and their respective oligomers, as flame retardant additives for polyamide fibers to impart fire resistance while maintaining or improving processing characteristics for melt spun fibers and fabrics, thereof.

1) FIELD OF THE INVENTION

The present invention relates to flame retardant polyamide fibers, wherein the flame retardant is incorporated as a molten polymer within the molten polyamide polymer when it is extruded as a fiber. The flame retardant is at least one phosphonate polymer, copolymer, and/or their respective oligomers. The inventive fibers may be blended in textile structures including non-thermoplastic flame retardant fibers, and not exhibit the ‘scaffolding effect’ which renders fabrics comprising flame retardant thermoplastic fibers flammable.

2) PRIOR ART

A number of approaches have been investigated to impart fire resistance to polyamide fibers with varying degrees of success. In general, it has been extremely challenging to impart fire resistance into polyamide fibers without detracting from fiber spinning efficiency, fiber quality, and mechanical properties. Many flame retardants are based on solids generally in the form of particles or powders. Another approach is to co-polymerize polyamide polymers to incorporate a flame retarding phosphorus monomer. These approaches, when incorporated into polymer and extruded as a fiber, have the above mentioned problems of reduced processability and reduced mechanical properties. Thus, there is a recognized need to provide fire or flame resistance to polyamide fibers without detracting from melt processability, strength, modulus, dyeing and heat-setting characteristics as compared to the unmodified polyamide.

Furthermore, those skilled the art of flame retarding fabric design and development know the dangers of blending flame retarding thermoplastic fibers with non-thermoplastic flame retarding fibers and creating a flammable fabric. The best known example is fabric comprising flame retardant polyester and flame retarding treated cotton fibers. This phenomenon is the well known ‘scaffolding effect’.

Protective garments comprising flame retardant (FR) fabrics are required to protect workers from flame and thermal hazards. Such workers can include chemical/petroleum, electrical workers, firefighters, race car drivers, police, and military personnel.

For a FR garment to offer protection, the fabric used must not sustain a flame, not melt and stick to the wear's skin, have minimal high temperature shrinkage, insulate the user, and offer resistance to fabric rupture leading to direct flame impingement upon the user.

Industry standards promulgated by the National Fire Protection Association (NFPA) govern single layer and multilayer flame and thermal protective clothing performance standards. Among these standards are:

NFPA1975: Standard on Station/Work Uniforms for Fire and Emergency Services (2004) NFPA 2112: Standard on Flame-Resistant Garments for Protection of Industrial Personnel Against Flash Fire (2007).

There are also standards governing fire protective clothing ensembles of more than a single fabric layer. Among these are:

NFPA 1951: Standard on Protective Ensembles for Technical Rescue Incidents (2013). NFPA 1971: Standard on Protective Ensembles for Structural Fire Fighting and Proximity Fire Fighting (2013). NFPA 1976: Standard on Protective Ensemble for Proximity Fire Fighting (2000). NFPA 1977: Standard on Protective Clothing and Equipment for Wildland Fire Fighting (2011).

In addition, other flame resistance requirements are set by the U.S. Military (GL-PD-07-12) for battle dress uniform and SFI Foundation for race car drivers.

Test Methods

Fire resistance may be tested by measuring after-burning time and degree of consumption. These test methods provide laboratory tests for comparing materials and to meet certain industry-mandated performance levels.

Some of the tests used to measure the flame and thermal resistance and protection potential of textile materials include:

For Industrial Apparel:

-   -   1. ASTM D6413: Standard Test Method for Flame Resistance of         Textiles (Vertical Test).     -   2. ASTM F2703—Standard Test Method for Unsteady-State Heat         Transfer Evaluation of Flame Resistant Materials for Clothing         with Burn Injury Prediction (Thermal Protective Performance         Test).     -   3. ASTM F1930: Standard Test Method for Evaluation of Flame         Resistant Clothing for Protection Against Flash Fire Simulation         Using an Instrumented Manikin.     -   4. ASTM D2863: Standard Test Method for Measuring the Minimum         Oxygen Concentration to Support Candle-Like Combustion of         Plastics (Oxygen Index).

For Transportation (Buses, Trains, and Aircraft):

-   -   1. FAR 25.853B Appendix F, Part 1—Aircraft     -   2. MVSS 302—Automobiles, Buses, RV's

Marine Vessels:

-   -   1. ASTM E136-12: Standard Test Method for Behavior of Materials         in a Vertical Tube Furnace at 750° C.

Carpets:

-   -   1. ASTM D2859: Standard Test Method for Ignition Characteristics         of Finished Textile Floor Covering Materials.     -   2. ASTM E84: Standard Test Method for Surface Burning         Characteristics of Building Materials.     -   3. ASTM E648-10e1: Standard Test Method for Critical Radiant         Flux of Floor-Covering Systems Using a Radiant Heat Energy         Source.     -   4. ASTM E662-13: Standard Test Method for Specific Optical         Density of Smoke Generated by Solid Materials.

Engineered Plastics:

-   -   1. UL 94, the Standard for Safety of Flammability of Plastic         Materials for Parts in Devices and Appliances testing.

The above tests use small specimens that are representative, to the extent possible, of the material or assembly being evaluated. The rate at which flames travel in various directions along surfaces depends upon the physical and thermal properties of the material, product or assembly under test, the specimen mounting method and orientation, the type and level of fire or heat exposure, the availability of air, and properties of the surrounding enclosure. If different test conditions are substituted or the end-use conditions are changed, it may not always be possible by or from these tests to predict changes in the fire-test-response characteristics measured.

The results from any flame or thermal performance test are valid only for the fire test exposure conditions described in each test method.

To meet industry standards, manufacturers developed numerous ‘engineered blends’ of fiber combinations wherein each fiber contributes particular functions such as preventing flame propagation and penetration, lowering fabric shrinkage at high temperatures, and controlling fabric melting and dripping. Fibers also contribute to functional features such as dyed colors, comfort, durability, and cost.

Currently, most common fire protective fabrics contain expensive fibers—particularly para- and meta- aramid fibers. These fibers are commercially available from several suppliers including DuPont Protective Systems which offers meta-aramid and para-aramid fibers under the trade names of Nomex® and Kevlar®. Unfortunately, garments comprising aramid fibers are often expensive and uncomfortable to wear.

Fabrics comprising nylon and cotton (NYCO) fabrics are used in many military and work wear uniforms not requiring flame resistance. These fabrics are durable, comfortable, and easy to maintain. Unfortunately, these fabrics do not possess the necessary flame and thermal resistance for fire protective garments.

It is possible to improve the flame resistance of fabrics comprising nylon and cotton fibers by applying a flame retarding finish to the formed fabric. These finishes may comprise phosphorus compounds which are char formers and particularly effective on cellulose fibers. Examples of fabric finishing are taught in US patents including:

4,145,463 Flameproofing Albright & Wilson Aug. 20, 1973 Textiles 4,154,878 No-dry process of Baitenger/Cotton May 15, 1979 applying phosphonium Incorporated salt precondensates to textiles 4,494,951 Flameproofing Albright & Wilson Jan. 22, 1985 Textiles

Today, the most often, durable flame retardant chemistries for cellulose fabrics are phosphorus-based FR chemicals which are incorporated into the cellulose fibers. A common method is the Proban® finishing process in which the cellulose fibers are impregnated with an organophosphorus pre-poly and crosslinked using ammonium gas. Flame retardant garments using this process are offered by Westex, Inc under the Ultrasoft® or Indura® trade names.

Ultrasoft fabrics are a blend of 88% cotton and 12% nylon fibers and treated using the Proban flame retarding finishing process. Ideally, for fabric strength and garment durability the nylon fiber content should be raised above the 12% level. However, when attempted, the fabrics lack adequate flame resistance.

There exists the need for a flame retardant polyamide fiber with sufficient flame resistance to contribute strength, abrasion resistance, and comfort in ‘engineered blends’ with other flame retardant fibers such as FR viscose, FR-treated cellulose (including cotton, bast, lyocell), FR wool, aramids, PBI, PBO, PSA, OPF, phenolic, melamine, modacrylic, and inorganic fibers.

Flame retardant fibers and fabrics are also required for other industry segments such as transportation wherein textile surfaces such as the carpeting, seating, curtains, bedding and wall coverings of buses, trains, aircraft, ships, and oil platforms.

Additives exist for rendering injection-molded polyamides polymers flame retardant. The recipes for such polyamide polymers may contain as little as 40% polyamide polymer with the balance comprising flame retardants of any particle size, inorganic fillers, pigments, lubricants, or glass fiber reinforcement. Clearly, flame retardants with no particle size restrictions are not suited for fiber spinning.

Among flame retarding compounds are additives such as melamine compounds rich in nitrogen to smother a flame or phosphorus compounds to form chars to block the flame. At one time, compounds such bromine or antimony were used, however, these types of chemicals can be toxic and can leach into the environment over time making their use less desirable. In some countries certain brominated additives and phosphorus salts are banned or under review because of environmental concerns.

The requirements for flame retarding polyamide fibers are stringent in part because of the high processing temperatures and sensitivity of the polyamides' melt viscosity and consequently melt-spinnability into fibers. Moreover, flame retardant polyamides must exhibit long-term dimensional stability, have good dyeing characteristics in the final fiber, exhibit good mechanical properties and permanent flame resistance. These challenges combined with environmental regulations for toxicity and mitigation of leaching of the flame retardant into the environment over time has made it extremely difficult to meet all of these requirements.

The hurdles are so high that one team of researches has written that,

‘It seems unlikely that there will be any major breakthroughs with regards to new and/or improved reactive flame-retardant (comonomers) or conventional organic or inorganic flame retardant additives for use in (either PET or) nylon fibers. The requirements to achieve satisfactory flame retardance without appreciably interfering with the spinning process, modifying the physical and mechanical properties of the fibres, or affecting long-term stability, and at economic cost, restricts options considerably’. [‘Flame-retardant polyester and polyamide textiles' by P. Joseph and J. R. Ebdol.’ Polyester and Polyamides, Edited by Deopura, et. al (published by Woodhead Publishing Limited, 2008), Page 320.]

Another problem facing inventors of flame retardant fabric blends is known as the ‘scaffolding effect’. This effect is described as ‘Conventional thermoplastic fibers like polyamide, polyester, and polypropylene will shrink away from an ignition flame and avoid ignition: this can give the fiber an appearance of flame retardancy when, in fact, if the shrinkage was prevented, they would burn intensely. This so-called scaffolding effect is seen in polyester-cotton and similar blends where the molten polymer melts on to the non-thermoplastic cotton and ignites. Similar effects are seen in composite textiles comprising thermoplastic and non-thermoplastic components.’ [‘Textiles’ by A. R. Horrocks, Fire Retardant Materials, Edited by Horrocks and Price (published by Woodhead Publishing Limited 2001), Page 148.]

This phenomenon is also recognized by P. Bajaj [‘Heat and Flame Protection’ Handbook of Technical Textiles', Edited by Horrocks and Anand (published by Woodhead Publishing Limited 2000), Page 240]: ‘Nylons have a self-extinguish property due to extensive shrinkage and dripping during combustion. Problems arise in blends with natural fibers, like cellulose which will char and form a supporting structure (the so-called scaffolding effect) which will then hold the molten polymer”.

What is needed is an improved thermoplastic polyamide fiber which may be used alone or in engineered fiber blends with flame resistant or non-flame resistant of fibers in textile structures and maintains the ability to self extinguish and meet an overall level of flame resistance for the system.

SUMMARY OF THE INVENTION

Embodiments are generally directed to a polymer fiber that includes a thermoplastic polyamide and at least one thermoplastic phosphorous containing polymer or oligomer. In various embodiments, the fire retardant polymer may be a phosphonate containing polymer, phosphonate containing copolymer, phosphonate containing oligomer, or combinations thereof. In certain embodiments, the polymeric fibers may include a polyphosphonate, copoly(phosphonate ester), copoly(phosphonate carbonate), and/or their respective oligomers and a polyamide.

Other embodiments of the invention are directed to polymer compositions including a polyphosphonate, copoly(phosphonate ester), copoly(phosphonate carbonate), and/or their respective oligomers and a polyamide that maintains acceptable melt processing characteristics as compared to the unmodified polyamide.

Other embodiments of the invention are directed to polymeric fibers including a polyphosphonate, copoly(phosphonate ester), copoly(phosphonate carbonate), and/or their respective oligomers and a polyamide that meets the standardized fire resistance ratings required for a variety of consumer and industrial products without detracting from other important safety, environmental, manufacturing and user requirements.

Still another embodiment if the invention is directed to polymeric fibers including a polyphosphonate, copoly(phosphonate ester), copoly(phosphonate carbonate), and/or their respective oligomers and a polyamide that may be blended with non-thermoplastic fibers and produce a textile structure which avoids the ‘scaffolding effect’ and self extinguishes after exposure to a flame.

DETAILED DESCRIPTION

It is to be understood that the terminology used in the description is for the purpose of describing the particular versions or embodiments only, and is not intended to limit the scope of the present invention, which will be limited only by the appended claims. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present invention, the preferred methods, devices, and materials are now described. All publications mentioned herein are incorporated by reference in their entirety.

It must also be noted that, as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural reference unless the context clearly dictates otherwise. Thus, for example, reference to “a combustion chamber” is a reference to “one or more combustion chambers” and equivalents thereof known to those skilled in the art, and so forth.

As used herein, the term “about” means plus or minus 20% of the numerical value of the number with which it is being used. Therefore, about 50% means in the range of 40%-60%. Further, all ranges include not only the beginning and ending numbers of a range, but every number in between, in any combination, as that is the very definition of a range.

The terms “flame retardant,” “flame resistant,” “fire resistant,” or “fire resistance,” as used herein, means that the composition exhibits a limiting oxygen index (LOI) of at least 27. “Flame retardant,” “flame resistant,” “fire resistant,” or “fire resistance,” may also refer to the flame reference standard ASTM D6413-99 for textile compositions, flame persistent test NF P 92-504, and similar standards for flame resistant fibers and textiles.

The term ‘self-extinguishing’ used herein means that a fibrous structure comprising the inventive flame retarding polyamide fiber will not continue to burn after the flame source is removed during test method ASTM D6413.

Embodiments of the invention are directed towards polymer fibers and flame retardant polyamides that include a thermoplastic polyamide and one or more phosphonate containing polymer, copolymer, or oligomer. Flame retardant polyamides of the present invention contain no halogen compounds.

The U.S Federal Trade Commission defines a polyamide fiber as: ‘A manufactured fiber in which the fiber forming substance is a long-chain synthetic polyamide in which less than 85% of the amide-linkages are attached directly (—CO—NH—) to two aliphatic groups’.

Useful polyamide polymers include, but are not limited to: Nylon 6, nylon 6-6, nylon 6-10 nylon 11, nylon 12, nylon 4-6, nylon 6-12, nylon 6-6T, nylon 6T, nylon 6I-6T, MXD6, or any combinations of these.

Embodiments of the invention are not limited by the type of phosphonate containing polymer, copolymer, or oligomer. For example, in various embodiments, the phosphonate containing polymer, copolymer, or oligomer may be derived from diaryl alkylphosphonates, diaryl arylphosphonates, or combinations thereof and an aromatic dihydroxy compound, such as dihydric phenols, bisphenols, or combinations thereof. Such phosphonate containing polymers, copolymers, or oligomers may be block copolymers having discrete phosphonate and carbonate blocks that are covalently attached to one another, or the phosphonate containing polymer, copolymer, or oligomer may be random copolymers in which individual phosphonate and carbonate monomers or small phosphonate or carbonate segments, for example, 1 to 10 monomeric units, are covalently attached.

In certain embodiments, phosphonate containing polymer, copolymer, or oligomer may be the polyphosphonate, copoly(phosphonate ester), copoly(phosphonate carbonate) as described and claimed in U.S. Pat. Nos. 6,861,499, 7,816,486, 7,645,850, and 7,838,604 and U.S. Publication No. 2009/0032770, each of which are hereby incorporated by reference in their entireties, or their respective oligomers. Briefly, such polymers and oligomers may include repeating units derived from diaryl alkyl- or diaryl arylphosphonates. For example, in some embodiments, such polyphosphonates or phosphonate oligomers may have a structure including:

where Ar is an aromatic group and —O—Ar—O— may be derived from a compound having one or more, optionally substituted, aryl rings such as, but not limited to, resorcinols, hydroquinones, and bisphenols, such as bisphenol A, bisphenol F, and 4,4′-biphenol, phenolphthalein, 4,4′-thiodiphenol, 4,4′-sulfonyldiphenol, or combinations of these, X is a C₁₋₂₀ alkyl, C₂₋₂₀ alkene, C₂₋₂₀ alkyne, C₅₋₂₀ cycloalkyl, or C₆₋₂₀ aryl, and n is an integer from 1 to about 100, 1 to about 75, or 2 to about 50, or any integer between these ranges.

In other embodiments, the copoly(phosphonate ester), copoly(phosphonate carbonate) and their respective oligomers may have structures such as, but not limited to:

and combinations thereof, where Ar, Ar¹, and Ar² are each, independently, an aromatic group and —O—Ar—O— may be derived from a compound having one or more, optionally substituted aryl rings such as, but not limited to, resorcinols, hydroquinones, and bisphenols, such as bisphenol A, bisphenol F, and 4,4′-biphenol, phenolphthalein, 4,4′-thiodiphenol, 4,4′-sulfonyldiphenol, or combinations of these, X is a C₁₋₂₀ alkyl, C₂₋₂₀ alkene, C₂₋₂₀ alkyne, C₅₋₂₀ cycloalkyl, or C₆₋₂₀ aryl, R¹ and R² are aliphatic or aromatic hydrocarbons, and each m, n, and p can be the same or different and can, independently, be an integer from 1 to about 100, 1 to about 75, 2 to about 50, or any integer between these ranges. In certain embodiments, each m, n and p are about equal and generally greater than 5 or greater than 10.

In particular embodiments, the Ar, Ar¹, and Ar² may be bisphenol A and X may be a methyl group providing polyphosphonates, copoly(phosphonate carbonate), copoly(phosphonate ester), and their respective oligomers. Such compounds may have structures such as, but not limited to:

and combinations thereof, where each of m, n, p, and R¹ and R² are defined as described above. Such copoly(phosphonate ester), copoly(phosphonate carbonate) and their respective oligomers may be block copoly(phosphonate ester), copoly(phosphonate carbonate) or oligomers thereof in which each m and n is greater than about 1, and the copolymers contain distinct repeating phosphonate and carbonate blocks. In other embodiments, the copoly(phosphonate ester), copoly(phosphonate carbonate) or their respective oligomers can be random copolymers in which each n can vary and may be from 1 to about 10.

The weight average molecular weight (Mw) of each of the one or more phosphonate containing polymers and copolymers, and in particular embodiments, the polyphosphonate, copoly(phosphonate ester), and/or copoly(phosphonate carbonate), in the polymer fibers and flame retardant polyamides of the invention can range from about 10,000 g/mole to about 120,000 g/mole measured against polystyrene (PS) standards. The Mw of the oligomeric phosphonates and cophosphonate oligomers can range from about 1,000 g/mole to about 10,000 g/mole measured against PS standards, and in some embodiments, the Mw can range from about 2,000 g/mole to about 6,000 g/mole measured against PS standards.

“Molecular weight,” as used herein, is, generally, determined by relative viscosity (η_(rel)) and/or gel permeation chromatography (GPC). “Relative viscosity” of a polymer is measured by dissolving a known quantity of polymer in a solvent and comparing the time it takes for this solution and the neat solvent to travel through a specially designed capillary (viscometer) at a constant temperature. Relative viscosity is a measurement that is indicative of the molecular weight of a polymer. It is also well known that a reduction in relative viscosity is indicative of a reduction in molecular weight, and reduction in molecular weight causes loss of mechanical properties such as strength and toughness. GPC provides information about the molecular weight and molecular weight distribution of a polymer. It is known that the molecular weight distribution of a polymer is important to properties such as thermo-oxidative stability (due to different amount of end groups), toughness, melt flow, and fire resistance, for example, low molecular weight polymers drip more when burned.

The thermoplastic polyamide used in various embodiments is not limited and can vary. For example, in some embodiments, the thermoplastic polyamide can be nylon 6, nylon 6-6, nylon 6-10, nylon 11, nylon 12, nylon 4-6, nylon 6-12, nylon 6-6T, nylon 6T, nylon 6I-6T, MXD6, or any combination of these. Other polyamides not specifically described are also encompassed by these embodiments and can be combined with the phosphonate containing polymers, copolymers, and oligomers described above to create polymer fibers or flame retardant polyamides of the invention.

The amount of the phosphonate containing polymer, copolymer, or oligomer mixed can vary among embodiments and may be modified based on the desired properties of the flame retardant polyamide. For example, in some embodiments, the amount of polyphosphonate, copoly(phosphonate ester), copoly(phosphonate carbonate) or their respective oligomer can be up to about 25% by weight relative to the host thermoplastic polyamide. In other embodiments, the amount of polyphosphonate, copoly(phosphonate ester), copoly(phosphonate carbonate) or their respective oligomer can be from about 1 wt. % to about 25 wt. %, about 2 wt. % to about 20 wt. % or about 5 wt. % to about 15 wt. % relative to the host thermoplastic polyamide.

In some embodiments, the polymer fibers and flame retardant polyamides may include additional additives that can be incorporated to improve one or more properties exhibited by the fiber or flame retardant polyamide or provide, for example, color. Non-limiting examples of such additional additives include fire resistant additives, fillers, dyes, antioxidants, viscosity modifiers, pigments, anti-dripping agents, wetting agents, lubricating agents, anti-static or conductive agents, anti-microbial, and other additives typically used with synthetic fibers. In particular embodiments, the polyamide fibers or flame retardant polyamides may include a dye and/or pigment. The fire resistant additives of such embodiments may include, but are not limited to, metal hydroxides, nitrogen containing flame retardants such as melamine cyanurate, melamine polyphosphonate, phosphinate salts, organic phosphates, other phosphonates, organic sulfonate salts, siloxanes, and the like.

In particular embodiments, the polymer compositions of the invention can be used, incorporated into, a non-woven or spun into yarns that can be used in woven, knitted, or tuffed textiles forms. For example, the polymer compositions of various embodiments may be used in textile products such as flame retarding clothing, carpet, flooring materials, bedding, upholstery, wall coverings, theater curtains, window treatments, wigs, and non-woven articles used in consumer products that must meet fire resistance standards. More particular exemplary embodiments include fabrics that are woven, knitted, or tuffed from polyamide thread or yarn that are used in apparel and home furnishings, such as shirts, pants, jackets, hats, bed sheets, blankets, upholstered furniture, carpets, theater curtains, window treatments, luggage, and the like. Non-woven fibers prepared from the polymer compositions of the invention can be used in other applications cushioning and insulating material in pillows, blankets, quilts, comforters, and upholstery padding. Other embodiments include industrial polyamide fibers, yarns, and ropes that are used, for example, in tire reinforcements, fabrics for conveyor belts, safety belts, airbags, coated fabrics, military or police equipment, and plastic reinforcements with high-energy absorption.

The fibers of various embodiments may have any thickness or diameter, and the diameter of fibers may vary by their intended use. For example, in embodiments in which the fibers are used in textiles for clothing, the fiber diameter may be less than fibers used for industrial fabrics or ropes, which may have a smaller diameter than fibers used for carpeting. In some embodiments, the fiber diameter may be from about 2.0 μm to about 50 μm, about 5 μm to about 40 μm, about 10 μm to about 30 μm, or from about 12 μm to about 25 μm. In other embodiments, the denier of the fiber may be from about 0.9 denier to about 30 denier, about 2 denier to about 25 denier, or 10 denier to about 15 denier. A “denier” is a well-known unit of linear density in the textile arts and is defined herein as the weight in grams of 9000 meters of a linear material.

Some embodiments of the invention are directed to other articles of manufacture incorporating the polymer compositions described above. For example, certain embodiments are directed to articles of manufacture such as, but not limited to, “plastic” bottles, films, tarpaulin, filters, insulation for wires, insulating tapes, and other films, moldings, and other articles including the polymer compositions. In other embodiments, fibers including the polymer compositions of the invention can be incorporated into fiber reinforced composites that include a matrix material that is compatible with the polymer compositions described above. In a fiber reinforced composite, the fibers of the invention may be the matrix resin with high temperature reinforcing fibers, or the reinforcing fiber with a lower melting temperature matrix resin. Such fiber reinforced composites may be incorporated into any of the articles described above. In still other embodiments, the polymer compositions described herein may be incorporated into wood finishes that can be applied to wood products as a liquid or gel.

Further embodiments of the invention are directed to methods for making the polymer compositions of the invention and methods for preparing articles of manufacture or fibers from the blended material. For example, some embodiments include methods for preparing a polymer composition including the steps of blending in a melt a thermoplastic polyamide and a phosphonate containing polymer, copolymer, or oligomer. The melt blending may be carried out by any mixing technique, for example, melt mixing may be carried out in a Brabender mixer or extruder. In some embodiments, the methods may include the steps of extruding the mixture after melt mixing and pelleting the resulting material. In other embodiments, the methods may include compressing the melt mixed material in rollers to create a film, slit film fibers, spin casting a film, or blow-molding a film. In still other embodiments, the methods may include molding the melt mixed material into an article of manufacture.

In particular embodiments, the melt mixed polymer composition of the invention may be spun into fibers by fiber spinning. In such embodiments, the solution viscosity of the melt mixed material may be modified to improve the processability of material during fiber spinning In particular, the relative viscosity of the polyamide polymer in formic acid may be from 18 to 100 when tested using ASTM 789: Standard Test Method for Determination of Solution Viscosities of Polyamides. In some embodiments, the solution viscosities may depend on the end application. For example, textile grade fibers may be prepared from a polymer composition having a relative viscosity of from about 20 to 50 and fibers for military equipment or industrial applications such as tire cord and monofilaments may have a relative viscosities exceeding 70. “Solution viscosity” as defined herein is the difference in time it takes for a polymer solution to pass through a capillary of specified length at a specific temperature versus the time it takes the pure solvent and can be measured according to method ASTM D5225.

In certain embodiments, conversion of molten polymer to fiber may be done in either a single step or a sequence of steps. Methods for the preparation of polymer fibers may include the steps of stretching, heat setting, crimping, and cutting the spun fibers. The term “heat setting” as used herein refers to thermal processing of the fibers in either a steam atmosphere or a dry heat environment. Heat setting gives fibers, yarns, or fabric dimensional stability and can provide other desirable properties such as higher volume, wrinkle resistance, and/or temperature resistance and increased tensile strength and modulus.

The polymer compositions, polymer fibers, articles of manufacture, and such described herein exhibit excellent flame resistance and a superior combination of properties including processing characteristics, mechanical properties, heat-setting characteristics, and ability to dye as compared to fiber compositions containing other flame retardants. Because the additives are polymeric or oligomeric, and form compatible mixtures with the host polyamides, they do not leach out and will generally not produce environmental concerns. Therefore, polymer compositions described herein including a thermoplastic polyamide and one or more polyphosphonates, copoly(phosphonate ester)s, copoly(phosphonate carbonate)s, and/or their respective oligomers meet all of the processing and performance requirements specified for polyamide fibers, and also overcome the environmental and toxicity considerations. Moreover, formulations containing these flame retardant materials were spun into high quality fibers, formed into test articles and tested for flame resistant properties.

Without wishing to be bound by theory, one plausible explanation for the unexpected behavior is that the polyphosphonate, copoly(phosphonate ester), copoly(phosphonate carbonate) or their respective oligomer may become incorporated into the polyamide chemically via transamidation or transesteramidation that can occur during high temperature processing. They may also become incorporated chemically via reaction of end groups present on the polyamide or polyphosphonate, copoly(phosphonate ester), copoly(phosphonate carbonate) or their respective oligomers. Such end groups may be ester, phosphonate, carbonate, or hydroxyl. Due to chemical incorporation, the chance of leaching is negated. Yet another possible explanation is that the polyphosphonate, copoly(phosphonate ester), copoly(phosphonate carbonate) or their respective oligomers may become entangled in the polyamide matrix. At the same time, the flame retardant materials satisfy the UL or similar standardized fire resistance requirements without detracting from important mechanical and processing properties. This is achieved by formulating a composition comprising a thermoplastic polyphosphonate, copoly(phosphonate ester), copoly(phosphonate carbonate) or their respective oligomers, and a polyamide which is subsequently melt spun into a fiber.

EXAMPLES

Although the present invention has been described in considerable detail with reference to certain preferred embodiments thereof, other versions are possible. Therefore the spirit and scope of the appended claims should not be limited to the description and the preferred versions contained within this specification. Various aspects of the present invention will be illustrated with reference to the following non-limiting examples.

Example 1

A compound comprising nylon 6-6 and 5% polyphosphonate flame retardant (Nofia HM 1100 from FRX Polymers) was melt blended and extruded into fibers.

The fibers were cut into ‘staple fibers’ and the fibers twisted into sliver strands of 6 grams per meter (84 grains/yard). Three fiber blends were prepared:

-   -   A. 100% Nylon 6-6 with FR polyphosphonate additive     -   B. A 50/50 blend of A with non-thermoplastic para-aramid fiber     -   C. A 50/50 blend of A with non-thermoplastic flame retardant         rayon fiber with the following results:         The three of each sliver were exposed to a flame for 12 seconds         with the follow results:

Sample After Flame, seconds Observations A 0 Fiber shrinkage 2 drips B 0 No Shrinkage 0 Drips C 0 No Shrinkage 0 drips Thus it is apparent that there has been provided, in accordance with the invention, a flame retardant polyamide that fully satisfies the objects, aims, and advantages set forth above. (A flame retardant nylon fiber with no scaffolding effect when blended with non-thermoplastic fibers.) While the invention has been described in conjunction with specific embodiments, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. 

1. A polymer fiber comprising: a thermoplastic polyamide; and at least one phosphonate containing polymer, copolymer, oligomer, or combination thereof.
 2. The polymer fiber of claim 1, wherein the thermoplastic polyamide comprises nylon 6, nylon 6-6, nylon 6-10, nylon 11, nylon 12, nylon 4-6, nylon 6-12, nylon 6-6T, nylon 6T, nylon 6I-6T, MXD6, or any combination of these.
 3. The polymer fiber of claim 1, wherein the phosphonate containing polymer, copolymer, oligomer, or combination thereof comprises at least one polyphosphonate, copoly(phosphonate ester), copoly(phosphonate carbonate), oligomeric phosphonates oligomeric cophosphonate esters, oligomeric cophosphonate carbonates, and combinations thereof.
 4. The polymer fiber of claim 1, wherein the phosphonate containing polymer, copolymer, oligomer, or combination thereof comprises repeating units derived from diaryl alkylphosphonate, diaryl arylphosphonate, and combinations thereof, and diphenyl methylphosphonate and aromatic dihydroxy compound.
 5. The polymer fiber of claim 1, wherein the phosphonate containing polymer, copolymer, oligomer or combination thereof comprises at least one polyphosphonate, copoly(phosphonate ester), or copoly(phosphonate carbonate) having a molecular weight of from about 10,000 g/mole to about 120,000 g/mole measured against PS standards.
 6. The polymer fiber of claim 1, wherein the phosphonate containing polymer, copolymer, oligomer or combination thereof comprises at least one oligomeric phosphonate, oligomeric cophosphonate ester, or oligomeric cophosphonate carbonate having a molecular weight of from about 1,000 g/mole to about 10,000 g/mole.
 7. The polymer fiber of claim 1, wherein the polymer fiber comprises about 1 wt. % to about 25 wt. % of the at least one phosphonate containing polymer, copolymer, oligomer, or combination thereof.
 8. The polymer fiber of claim 1, further comprising one or more fire resistant additives, fillers, delusterants, dyes, antioxidants, viscosity modifiers, pigments, anti-dripping agents, lubricants, wetting agents, anti-microbials, or combinations thereof.
 9. The polymer fiber of claim 1, wherein the polymer fiber comprises a fiber diameter of from about 2 μm to about 60 μm.
 10. The polymer fiber of claim 1, wherein the polymer fiber comprises a fiber denier of from about 0.9 denier to about 30 denier.
 11. The polymer fiber of claim 1, wherein the polymer fiber exhibits a limiting oxygen index (LOI) of at least
 27. 12. The polymer fiber of claim 1, wherein the material from which the polymer fiber was made exhibits an Underwriters Laboratory-94 (UL-94) of V-0 measured at a thickness of 0.8 mm.
 13. An article of manufacture employing the polymer fiber of claim 1, wherein the article of manufacture comprises fire retarding clothing, military or police equipment, carpet, flooring materials, wigs, and non-woven articles.
 14. The article of manufacture of claim 13, wherein the article of manufacture comprises flame retarding bottles, films, tarpaulin, filters, dielectric films, insulation for wires, insulating tapes, moldings, shirts, pants, jackets, hats, bed sheets, upholstered furniture, tapestries, wall coverings, curtains, insulating material, pillows, blankets, quilts, comforters, luggage, ropes, tire reinforcements, fabrics for conveyor belts, tires, safety belts, coated fabrics, or plastic reinforcements with high-energy absorption upholstery padding.
 15. A fabric comprising fibers of claim
 1. 16. A yarn comprising the fibers of claim
 1. 17. A staple fiber comprising the fibers of claim
 1. 18. A garment made from the fabric of claim
 15. 19. A fabric of claim 15 which self-extinguishes in an ASTM D6413 vertical flammability test. 